1. Field of Invention
The present invention relates to a metal oxide or mixed-metal oxide catalyst for hydrogen generation from metal borohydride. The invention also relates to a method of making, sintering, activating a metal oxide catalyst, regenerating a deactivated metal oxide catalyst, and the use of the catalyst for oxidative reaction on various chemical systems.
2. Description of the Related Art
Transition metal oxides have been employed as a catalyst in a variety of chemical processes, such as oxidation (U.S. Pat. No. 6,124,499), NOx treatment (U.S. Pat. No. 6,916,945), oxidation and ammoxidation of an alkane (U.S. Pat. No. 6,777,571), transesterification (U.S. Pat. No. 5,350,879) and oxidative coupling of methane (U.S. Pat. No. 4,826,796). Nonetheless, metal oxides or mixed-metal oxides have not been investigated or used for the application of hydrogen generation from metal borohydride solution in our best knowledge. On the whole, the catalytic activity of the metal oxides is closely associated with preparation conditions, electronic structures, degree of crystallization, oxidation states, surface area, and so on. Furthermore, the careful control of surface structures, compositions, phase or particle sizes of the metal oxides may play a critical role for diverse chemical catalyses.
Hydrogen is one of fundamental gases, which is largely necessitated in synthetic chemical companies. In aspect of clean energy, hydrogen has been gained much attention for the applications of fuel cells, hydrogen combustion engines, turbines etc. Due to recent increasing demands of hydrogen gas, several different methods of hydrogen storage systems have been developed, which include compressed or liquefied hydrogen, H2 adsorption on carbon nano-tube, activated carbon, or metals or mixed metal alloys. Compressed or liquefied H2 is relatively easy to control the H2 flow rate and pressure, but involves potential safety issues. The adsorption methods for H2 storage also have many problems including low hydrogen density per unit volume, deterioration of the materials, and slow response time for H2 generation, etc. Recently, hydrogen generation from aqueous borohydride solution using a catalyst has stirred many interests in scientific communities since it is not only stable in normal operation condition, but also releases hydrogen gas in safe and controllable way.
It has been widely known that hydrogen gas is generated by hydrolysis of sodium borohydride in the aid of acid, transition metals, or their salts (Kaufman, C. M. and Sen, B., J. Chem. Soc. Dalton Trans. 1985, 307-313). U.S. Pat. No. 6,534,033 disclosed that a transition metal catalyst was employed to generate hydrogen gas from a stabilized metal borohydride solution. Those metal catalysts, such as ruthenium, rhodium, or cobalt metal supported on various substrates exhibited high activity for hydrogen generation. Other metal catalysts, including silver, iron, nickel, copper, and so on are often inactive or less active for hydrogen generation at room temperature based on unpublished tests. Some metal catalysts such as copper and nickel, showed improved activity after they were heated in nitrogen at 600-800 degree C. Usage of high performance metal catalyst, such as ruthenium, rhodium or platinum, is cost prohibitive for one-time use in various applications.
According to a recent publication (Kojima, Y. et al., Int. J. Hydrogen Energy, 2002, 27, 1029-1034), Toyota Central R&D Laboratories, Inc. reported that a catalyst containing platinum and LiCoO2 has a high catalytic activity for hydrogen generation due to the synergistic effects of finely divided platinum metal on the metal oxide framework. However, this system still uses a precious metal like platinum, which is not attractive for practical application due to high production cost. From a practical point of view, a high performance catalyst for hydrogen generation having low production cost is highly advantageous.